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Your search keyword '"Melo Jorge, M. E."' showing total 17 results
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17 results on '"Melo Jorge, M. E."'

5. Incorporation of N in TiO2 films grown by DC-reactive magnetron sputtering

Author

Sério, S., Melo Jorge, M. E., Nunes, Y., Barradas, N. P., Alves, E., and Munnik, F.

Subjects
Ion beam analysis, Sputtering, N-doping TiO2, Band gap tuning
Abstract

Photocatalytic properties of TiO2 are expected to play an important role on emerging technologies based on OH radicals to destroy harmful nonbiodegradable organic and inorganic contaminants in water. The drawback is the wide band gap of TiO2 (3.2 eV) limiting its use to the UV part of electromagnetic spectrum under sunlight. Therefore, modifications of TiO2 are needed to tune the gap in order to allow an efficient use of the entire solar spectrum. One possibility is N-doping of TiO2 to make the photocatalytic activity possible under visible light and more suitable for water treatment. In our study nitrogen-doped TiO2 (TiO2-xNx) films were deposited by DC-reactive magnetron sputtering using a dual-magnetron co-deposition apparatus on unheated glass and silicon substrates using a pure titanium target. The depth profile of nitrogen was measured with heavy ion elastic recoil detection analysis combined with Rutherford backscattering spectrometry (RBS) and correlated with the optical and structural properties obtained by UV–VIS spectroscopy and X-ray diffraction (XRD).

Published
2012

12. A Possible Growth Mechanism for ZnO-TiO2 Composite Nanostructured Films Prepared by Electrodeposition.

Author

Frade, T., Melo Jorge, M. E., Fernández, B., Pereiro, R., and Gomes, A.

Subjects
NANOCOMPOSITE materials, FLUORINE, TIN oxides, NANORODS, NANOPARTICLES, CRYSTAL growth
Abstract

ZnO-TiO2 composite nanostructured films were successfully prepared on fluorine doped tin oxide conducting glasses, from aqueous solutions, using a two-step electrochemical deposition process. The architecture of the ZnO nanorods arrays was strongly modified by the presence of TiO2 nanoparticles either on the seed layer formation or during the growth process, although the solution stirring parameter also contributed to the film arrangement. ZnO nanorods with well-defined hexagonal facets (002) were grown almost vertically over the entire substrate if no solution stirring was used during growth process. The formation of flower-like ZnO nanorods, consisting of many aggregative nanorods, requires the presence of TiO2 nanoparticles on the seed layer formation or during the growth process. In this case, the clusters of one-dimensional ZnO nanorods forming flowers were made up of numerous hexagonal straight nanorods and small clusters/agglomerates of TiO2 particles. The results showed that the diameter and length of the flower-like ZnO nanorods increased with solution stirring and, on the other hand, decreased with increase of TiO2 nanoparticles content in the bath. A possible crystal growth mechanism of ZnO and ZnO-TiO2 nanocomposites is suggested. [ABSTRACT FROM AUTHOR]

Published
2014
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13. Hierarchically Grown CaMn3O6Nanorods by RF Magnetron Sputtering for Enhanced Visible-Light-Driven Photocatalysis

Author

Barrocas, B., Sério, S., and Melo Jorge, M. E.

Abstract

CaMn3O6films with hierarchical nanostructures were deposited for the first time on unheated quartz glass substrates by the radio frequency (RF) magnetron sputtering technique using a polycrystalline CaMnO3sample as sputtering target, and their photocatalytic activity was evaluated on the decolorization of Rhodamine 6G (Rh6G) aqueous solutions. The films scanning electron microscope (SEM) images evidence a growth of nanorods (NRs) arrays with planar endings and a narrow size distribution centered at about 30 nm in diameter. The CaMn3O6films surface is uniform and presents a high density of nanorods (116 nanorods per μm2). The high surface area combined with the tunnels crystallographic structure, evidenced by X-ray diffraction (XRD), results in an effective photocatalyst for Rh6G degradation under visible light irradiation. Based on the photodegradation experiments, it is suggested that a process of dye self-sensitization can be one of the key factors of the superior photocatalytic performance of CaMn3O6NRs. The kinetics of photocatalytic degradation of Rh6G follows a first-order reaction. Furthermore, XRD of the used films did not reveal additional phases indicating high photochemical stability, and the diffuse reflection infrared Fourier transform spectrum (DRIFT) does not show adsorbed organic species on the CaMn3O6NRs surface. This work provides a potential route to develop high-performance immobilized nanostructures, and the achievements open up many possibilities to tailor visible light active materials for environmental applications.

Published
2014
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14. Visible-Light Photocatalysis in Ca0.6Ho0.4MnO3Films Deposited by RF-Magnetron Sputtering Using Nanosized Powder Compacted Target

Author

Barrocas, B., Sério, S., Rovisco, A., and Melo Jorge, M. E.

Abstract

A novel immobilized Ca0.6Ho0.4MnO3photocatalyst has been developed with high photocatalytic activity for Rhodamine 6G (Rh6G) photodegradation under visible light irradiation. The nanocrystalline Ca0.6Ho0.4MnO3films were successfully deposited by RF-magnetron sputtering on unheated quartz glass substrates using Ca0.6Ho0.4MnO3powder as sputtering target and its photocatalytic functionalities have been explored. The visible-light-responsive photocatalytic activity of Ca0.6Ho0.4MnO3films was evaluated by the photodegradation of Rh6G aqueous solutions under visible light irradiation. The reusability of Ca0.6Ho0.4MnO3films on fresh dye samples was studied, showing an efficient reuse, without decreasing the photocatalytic decolorization efficiency. Furthermore, X-ray diffraction of the reused films did not reveal additional phases indicating high photochemical stability of the films even after reusing them in successive runs. The photocatalytic efficiency of the nanocrystalline Ca0.6Ho0.4MnO3films was further compared with TiO2films also produced by sputtering and the results revealed a significant improvement in photocatalytic activity over TiO2under visible light irradiation. Almost complete photodecolorization of a 5 ppm Rh6G solution was achieved in 4 h, while only 64% of dye degradation was observed in TiO2photoassisted process. This work provides a feasible route to fabricate high-performance immobilized ABO3-based nanomaterials, and the finding opens up a new venue for designing visible light sensitive ternary compounds for photocatalytical applications.

Published
2014
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17. Characterization and electrochemical behaviour of nanostructured calcium samarium manganite electrodes fabricated by RF-Magnetron Sputtering.

Author

Barrocas, B., Sério, S., Rovisco, A., Nunes, Y., de Sá, A. I., da Silva Pereira, M. I., and Melo Jorge, M. E.

Subjects
*ELECTROCHEMISTRY, *CALCIUM compounds, *SAMARIUM, *MANGANITE, *MAGNETRON sputtering, *X-ray diffraction, *IMPEDANCE spectroscopy
Abstract

Ca1-xSmxMnO3(0≤x≤0.4) films were successfully fabricated on Indium Tin Oxide (ITO) coated quartz glass substrates by radio frequency magnetron sputtering technique (RF- magnetron sputtering) from compacted nanosized powder targets, and subsequent annealing at 800°C in air, for 6h. X-ray diffraction shows a pure typical perovskite phase forx≥0.1. Scanning electron microscopy and atomic force microscopy revealed that the films surface is dense, with low roughness, depending on the Sm content, even though a few cracks were observed. Crystallite size was found to decrease with the Sm content. The electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The oxide electrode's capacitance was estimated using both techniques and the corresponding roughness factors evaluated. The values obtained from the two methods show a good agreement. A comparison between the voltammetric data and those referred in the literature allowed finding out that the redox reaction occurring at the electrode surface involves the pair Mn4+/Mn3+. EIS measurements confirm the voltammetric data and they also give additional information about the film porosity and the charge transfer resistance. This last parameter is associated with the oxidation and reduction of the pair Mn3+/Mn4+and after normalized by the roughness factor shows an increase with samarium content. [ABSTRACT FROM AUTHOR]

Published
2014
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